Febktjaky 5, 1904.] 



SCIENCE. 



213 



ence to the chemotropic and galvanotropie 

 reactions. 



Amitosis in the Embryo of Fasciolaria: 

 Heney Leslie Osboen,. Hamline Uni- 

 versity, St. Paul, Minnesota. (Read by 

 title.) 



Very early embryos of Fasciolaria ex- 

 hibit amitosis, a fact of interest because 

 direct nuclear division is seldom seen in 

 embryos. The embryos are in the gastrula 

 stage, the various organs of the head, foot 

 and visceral regions not yet having begun 

 to put in an appearance. The Fasciolaria 

 embryo is very peculiar in being greatly 

 dilated by the large number of primitive 

 ova which it has swallowed to serve as food. 

 Each of these ova is a large mass of small 

 yolk grains enclosed by a distinct cell wall 

 and permeated by cytoplasm containing 

 nuclei. The endoderm is composed of 

 cubical cells in which one sees nuclei in all 

 stages of direct division. In addition to 

 the ordinary form of amitosis, one also sees 

 here certain very large nuclei, constricting 

 at various points as if in an act of giving 

 rise to nuclei by gemmation. Mitotic fig- 

 ures are also seen in the endoderm. A 

 part of the endoderm of the embryo soon 

 becomes much enlarged and vacuolated, 

 and is evidently the seat of active secretory 

 processes connected with the digestion of 

 the yolk. The amitosis can thus be con- 

 sidered as coming in line with Ziegler's 

 view that it is an accompaniment of secre- 

 tory activity in the cells, but it is not in 

 accord with that part of his theory which 

 attaches amitosis to cell senescence. The 

 embryo possesses peculiar external organs, 

 the larval kidneys, which gradually assume 

 a large size, though purely provisional 

 structures. They lie directly under the 

 velum and are made up of ectodermal cells 

 swollen to huge dimensions by the accumu- 

 lation within them of a homogeneous, 

 faintly-staining material. It is generally 



supposed that these are excretory organs. 

 In the outer ends of the cells one finds 

 strong indications of amitosis. Here, of 

 course, amitosis is occurring in cells which, 

 though an important part of the body of 

 the larva for the time being, are in reality 

 secretory cells and not destined subse- 

 quently to give rise to new cells. Nuclear 

 divisions are found in the food-ova, which 

 are plainly degenerative, and the ova soon 

 after break up and lose their identity al- 

 together. These nuclear divisions appear 

 to be amitotic. They are clearly connected 

 with cell senescence. 



*0n the Morphology of Artificial Par- 

 thenogenesis in the Sea-urchin, Ariacia: 

 S. J. Hunter, University of Kansas. 

 The unfertilized eggs of Arhacia sub- 

 jected to the influence of sea water concen- 

 trated by evaporation to three fourths its 

 normal volume for about two hours may, 

 when transferred to sterilized sea water, 

 develop into free-swimming plutei. The 

 subsequent behavior of the eggs is depend- 

 ent upon the stage of maturation attained 

 when placed in the concentrated solution. 

 Both cytoplasm and nucleus are concerned 

 in development. Eggs isolated and placed 

 under continuous observation until blastu- 

 lation at first become amoeboid, nuclear 

 division following, sometimes repeated sev- 

 eral times before cleavage of cytoplasm 

 occurs. Cleavage is not total nor progress- 

 ive, partial or complete fusion of blas- 

 tomeres intervening. Cleavage prior to 

 blastulation is at no time comparable with 

 normal processes. Different embryos show 

 wide variations in character of external 

 changes. At blastulation ectoderm cells 

 are formed over large cells, generally three 

 in number. The blastula does not become 

 ciliated and free-swimming before nine 

 hours. Mesenchyma cells are thrown off 

 from the vegetable pole into the blastocoele. 

 The amoeboid activity spoken of begins at 



